Switchover system to provide antenna protection and space diversity configuration



Dec. 2. 1969 T. L. LEMING 3,482,165

SWITCHOVER SYSTEM TO PROVIDE ANTENNA PROTECTION AND SPACE DIVERSITYCONFIGURATION Filed Sept. 18, 1967 MAI N MODULATED TRANSMITTER BASEBANDssa'ae E STANDBY TRANSMITTER 20 RECEIVER BASEBAND SIGNAL COMBINERRECEIVER L RECEIVER FIG I PRIOR ART 26 I I 27a 2/ 27b 28b TRANSMITTERDETECTOR I EJETECTOR ANTENNA AUTOMATIC EIT'Ea A Is I I 29 85E$L ITRANSMITTER I BQPSI-m SGNAL RECEIVER SOURCE l F I 2 Q MREIQIIPT ER G 2BASEBAND I SIGNAL COMBINER RECEIVER REC INVENTOR. THOMAS L. LEMINGUnited States Patent G 3,482,165 SWITCHOVER SYSTEM TO PROVIDE ANTENNAPROTECTION AND SPACE DIVERSITY CON- FIGURATION Thomas L. Leming,Richardson, Tex., assignor to Collins Radio Company, Cedar Rapids, Iowa,a corporation of Iowa Filed Sept. 18, 1967, Ser. No. 668,552 Int. Cl.H041) 7/02 U.S. Cl. 325-56 8 Claims ABSTRACT OF THE DISCLOSURE Amicrowave antenna and transmitter switchover configuration including atleast two antennas and at least two transmitters connected to feedseparate antennas. Switchover control gives shutoff of an operatingtransmitter and antenna combination and simultaneous activation of andtransmission by another transmitter and antenna combination asautomatically initiated by antenna reflected power sensed above apredetermined level as would occur consistent with increasing VSWR withantenna damage.

This invention relates in general to transmitter to antenna switchover,and in particular, to an antenna and transmitter switchover system ascontrolled by reflected power (a .measure of VSWR) from an antenna beingused to switch antennas being fed and to simultaneously switchtransmitters being used.

With long distance microwave communication systems in order to increasepropagation reliability some users, particularly in the industrialmicrowave bands, have resorted to space diversity configurations. Abasic weakness with some such configurations is that both a maintransmitter and a standby transmitter are on only one of two or possiblymore available antennas and, in the event of damage to the antennaproviding transmitter service the system operation is disrupted eventhough a satisfactory second antenna is available. With these systemsusing a main and a standby transmitter a switchover control systemnormally provided senses transmitter power and modulation to determinethat appropriate drive to the antenna is available and to activateswitchover between transmitters. A major railroad using such a systemthrough a one-year period experienced virtually no equipment orpropagation outages aside from antenna failures on a route extendingfrom Los Angeles to Portland via Salt Lake City with, however, outagesattributable to this problem amounting to a total of approximately fiftyhours.

It is, therefore, a principal object of this invention to provide amicrowave system antenna and transmitter switchover configuration withtransmitters circuit connected to feed different antennas.

A further object with such an antenna and transmitter feed system is fortransmitter and antenna switchover to be controlled by reflected powerfrom an antenna being used.

Another object with such an antenna and transmitter feed system is forantenna reflected power induced auto matic switchover to be one way fromthe transmitter and antenna initially set and used and to provide manualreset in order to preclude any undesired, mechanical multivibratoraction.

Features of the invention useful in accomplishing the above objectsinclude, in various embodiments, a microwave antenna and transmitterswitchover configuration including at least two antennas and at leasttwo transmitters connected to feed separate antennas when the respectivetransmitters are individually in operation. One

Patented Dec. 2, 1969 "ice of the transmitters is a normally used maintransmitter and the other transmitter a standby transmitter. Aswitchover control is provided for shutoff of an operating transmitterand simultaneous activation of and transmission 'by the other antenna tothereby accomplish switch in transmitted signal feed from one antenna toanother antenna, and with this control circuit automatically controlledby a reflective power input sensed and a predetermined level detectedfor actuating control of the automatic switchover circuit. Generally, anantenna not being used in the transmit mode of operation is employed ina receive mode in such microwave station towers.

A specific embodiment representing what is presently regarded as thebest mode of carrying out the invention is illustrated in theaccompanying drawing.

In the drawing:

FIGURE 1 represents a prior art block schematic showing of a typicalantenna microwave tower installation typical of many of those that havebeen utilized heretofore; and,

FIGURE 2, a block schematic of an improved microwave antenna towerinstallation with a combined transmitter and antenna switchover systemproviding antenna protection and space diversity utilization betweenantennas of the tower.

Referring to the drawing:

The prior art typical antenna microwave installation of FIGURE 1 shows amodulated baseband signal source 10 connected for supplying a signalinput to a main transmitter 11 and a standby transmitter 12 both ofwhich operationally transform the baseband signal input thereto to amicrowave transmitter output signal. This signal is passed from the maintransmitter or standby transmitter, as the case may be, that isactivated and switch selected to and through switch 13 to a microwavecirculator junction 14 and from the circulator junction 14 to the topantenna structure 15. When antenna 15 is used in the receive modemicrowave RF signals received thereby are passed by the circulator 14 toand through an additional circulator 16, having a side port terminationin an impedance to minimize reflective signal buildup from such sideport, and on through another port to receiver 18 having a resultantoutput passed to combiner circuit 19 with a combined output ultimatelypassed to a baseband signal receiver and utilizing circuit 20. A secondantenna 21 similar in many respects to the antenna 15 but used solely inthis configuration as a receiving antenna passes received microwavesignals to a circulator 22 having an impedance terminated side port 23and an output from another circulator 22 port. The received microwavesignalling is passed from circulator 22 to receiver 24 resulting; in anoutput passed to combiner circuit 19 from which, in combination withsignalling, if any, from receiver 18 the combined output is passed tothebaseband signal receiver 20. Please note that a switchover controlsystem would be normally utilized with this typical installation subjectto activation by sensed transmitter power and modulation of theoperating transmitter 11 or 12, as the case may be, to initiate warm-upshould a standby or non-used transmitter not be maintained in acontinuously warmed up ready state. This is with such timed activationof switch 13 to switch after a warm-up interval from the transmitterbeing used to the previously unused transmitter when the switchovercontrol system is activated for such switching based on predeterminedtransmitter power and/or modulation sensed value levels.

'With applicants improved microwave antenna tower installation of FIGURE2, components the same and substantially the same or quite similar aregiven the same numbers or primed numbers as a matter of convenience asthe case may be. With this improved combined transmitter and antennaswitchover system providing antenna protection and space diversityutilization between antennas normally mounted on a microwave tower,modulated baseband signal source is connected for supplying a signalinput to a main transmitter 11' and a standby transmitter 12' with bothcapable of operationally transforming the baseband signal input theretoto a microwave transmitter output signal. The signal output passed fromthe main transmitter 11' is passed through microwave circulator 14 tothe top antenna structure 15, or if the standby transmitter 12' isoperating to and through circulator junction 25 to the lower antennastructure 21. Whenever antenna 15 or antenna 21 or both aresimultaneously used in the receive mode microwave RF signals received byone or both are passed by circulator 14 or circulator 25 or bothsimultaneously, as the case may be, through receive signal output portsof the respective circulators to receiver 18' or receiver 24' orsimultaneously both generating receiver output signalling passed to acombiner circuit 19' having an output passed to baseband signal receiver20.

A transmitter-antenna automatic switchover, latch, and reset controlcircuit 26 is included with applicants improved microwave antenna towerinstallation as shown in FIGURE 2 that is subject to transmitteractivation switchover control by a predetermined level signal inputthereto. Control circuit 26 has controlling circuit line connection tothe main transmitter 11 and also to the standby transmitter 12 for thetransmission of switchover control voltage from one of the lines to theother in accomplishing switchover control from one transmitter to theother. Signal directional couplers 27a and 27b are mounted in operativeassociation with the portion of the transmission line connected to therespective antennas 15 and 21 at such a location along the respectivetransmission lines between the respective circulators 14' and 25 andtheir antennas 15 and 21' as a function of signal phase so as tominimize signal coupling from the transmission lines relative to signalsin the transmit direction and to maximize the sensing of reflectedsignal power from the antenna through the respective transmission lines.The directional couplers 27a and 2712 are connected for feeding a sensedsignal input to detector units 28a and 28b, respectively, having in turndetected output line connections as inputs to control circuit 26. Thisprovides for feeding of directional coupler sensed signalling withrespect to the transmission line of an activated transmitter and itsantenna as rectified by a detector supplying a signal input to thecontrol circuit 26. Please note that the control circuit 26 may includeautomatically induced switchover latching so that once switchover hasoccurred reset may be accomplished only by manual means as for examplewith a manual reset 29 provided with the control circuit 26 so as topreclude any mechanical multivibrator action. Please note further, ifthe switchover control were always to be from the main transmitter 11'and its associated antenna 15 to standby transmitter 12' and itsassociated antenna 21' that only the directional coupling 27a anddetector device 28a would be required for deriving a controlling levelsignal input to the control circuit 26 in achieving the desiredswitchover action. However, with the structure shown, what wouldotherwise be the standby transmitter 12 and its associated antenna 21'could actually be the initially activated antenna subject todeactivation with switchover via the control circuit 26 with apredetermined signal level sensed by the directional coupler 27b and asrectified by detector device 28b.

Applicants protection system as a workable and dependable sytem isdependent upon variation in the return loss of the antenna system. Innormal installations where due care has been exercised, the antennafeedline would be expected to provide an output from the transmitter aspassed to and through a transmission line and reflected from the antennawith a VSWR of less than 1.10. This is equivalent to a 26.5 db returnloss; that is, the power reflected back from the antenna sytem towardthe equipment would be 26.5 db below the transmitter power. In the eventof antenna damage the VSWR normally may be expected to rise greatly; forinstance, in excess of 2.0, in which case the return loss would bereduced to approximately 9.5 db. Obviously, as the antenna damagebecomes greater from whatever cause, the return loss decreases, that is,less of the transmitted power is actually transmitted by the antennawith a greater portion of this transmitter output power being reflectedback from the antenna system as such so that at a 10.0 VSWR, almost allof the power is returned in the form of reflected power from the antennasystem. The detector devices 28a and 2812 are signal coupled to therespective transmission lines by directional couplers 27a and 27b thatare capable with proper location and design relative to the transmissionlines they are in operative association with of generally providing atleast 20 db directivity. The detector devices 28a and 281) are either soselected or adjustably set so that the threshold for switchover fallswithin a desired range normally that which would allow a VSWR ofsomething in the order of approximately 1.8 as that generating a sensedsignal level such as to cause antenna-transmitter switchover. Pleasenote at this point that this is so set as to exceed normally encounteredVSWRs of as much as 1.4 that occur on occasion by causation such as ofmoisture on a radome or water on a transmitter feed. Please notefurther, switchover systems such as have been employed herebefore,although not shown, that sense transmitter power and/or modulation forinitiating switchover may still be used in various supplementalcombinations with applicants improved switchover system.

Whereas this invention is here illustrated and described with respect toa specific embodiment thereof, it should be realized that variouschanges may be made without departing from the essential contributionsto the art made by the teachings hereof.

I claim:

1. In an antenna and transmitter switchover system, at least twoantennas; at least two transmitters connected by individual transmissionline means to feed separate antennas; control means .connected to atleast two transmitters and normally set for maintaining only one of saidtransmitters and one of said antennas in the transmit mode of operationat a time; antenna and transmission line reflected power sensing meansin operative association with the transmission line meansinterconnecting one of the transmitters and one of the antennas; saidcontrol means, signal connected to said sensing means and beingpredetermined level responsive to the signal sensed by said reflectedpower sensing means to initiate switchover activation from onetransmitter and antenna combination to another.

2. The antenna and transmitter switchover system of claim 1, includingan RF receiver for each antenna; and wherein an individual circulatorjunction having a received signal output port connection to one of saidreceivers is included in the individual transmission line means oftransmitter and antenna combinations.

3. The antenna and transmitter switchover system of claim 2, whereinoutput connections of multiple receivers are connected to a combinercircuit having an output connection to a baseband signal receiver.

4. The antenna and transmitter switchover system of claim 2, whereinsaid reflected power sensing means is mounted in operative associationwith the portion of transmission line means between a circulatorjunction and an antenna.

5. The antenna and transmitter switchover system of claim 4, whereinsaid antennas and transmitters are designed to be usable in a microwavecommunication system with, a modulated baseband signal source connectedfor supplying an input to the transmitters; with the transmitters beingof the type transforming, when selectively in operation, the basebandsignal input thereto to a microwave transmitter output signal; and withmultiple receivers connected to a common combiner circuit having anoutput connection to a baseband signal receiver.

6. The antenna and transmitter switchover system of claim 4, whereinsaid reflected power sensing means includes, a directional coupler; anda detector connected between the directional coupler and said controlmeans.

7. The antenna and transmitter switchover system of claim 6, wherein atleast two said reflected power sensing means are used in operativeassociation, individually, with the transmission line means of at leasttwo respective transmitter-antenna combinations.

8. The antenna and transmitter switchover system of claim 6, whereinsaid control means is an automatically actuated,with a predeterminedcontrolling input signal level, switchover latched control device withmanual reset.

References Cited UNITED STATES PATENTS ROBERT L. GRIFFIN, PrimaryExaminer 10 JAMES A. BRODSKY, Assistant Examiner U.S. Cl. X.R.

